Key Takeaways

• SL-RAT sewer technology sends an acoustic signal through a pipe and scores it 0 to 10 based on the flowability of the pipe
• A two-person crew can screen 20,000 thousand of feet per day, without flow contact or confined space entry
• Screening costs a fraction of the cost of cleaning
• Acoustic assessment is an order of magnitude faster than CCTV, making full-system assessment practical
• Results let a utility stop cleaning pipes that are already clear and focus crews where it matters
• Catching a blockage early reduces overflow risk and compliance headaches
• SL-RAT works best inside a larger condition-based maintenance program, not as a standalone fix

SL-RAT sewer technology uses sound waves to detect pipe blockages in minutes, helping utilities screen entire collection systems without CCTV trucks or manhole entry.

Every collection system manager runs into the same math problem. There are more miles of pipe than budget to inspect them all with a camera truck, and a fixed cleaning schedule often sends crews to pipes that were already clean while real problems sit unnoticed. Acoustic Assessment using SL-RAT sewer technology closes that gap by letting a utility screen the whole system acoustically first, then send the expensive tools only where the data points.

This article covers how Acoustic Assessment works, how it compares to CCTV, and what a mature acoustic screening program looks like once the data feeds into a real repair plan.

What Is the SL-RAT and How Does It Work?

The Transmitter and Receiver Setup

The SL-RAT works on a simple acoustic principle. A transmitter at one manhole sends a scientifically-designed sound signal down the pipe, and a receiver at the next manhole listens for what arrives. A clean, open pipe carries sound through with little loss. Anything that interferes with the flow of water also changes the quaility of the sound.

Reading the Score

That difference becomes a score from 0 to 10. Scores of 7 and above mean the line is flowing freely. A low score, often below a 5, flags a segment worth a closer look, whether that means a camera, cleaning, or repair. The assessment takes minutes, and a two-person crew can cover thousands of feet in a shift without confined space entry.

Acoustic Assessment vs. CCTV Inspection: Cost, Speed, and Safety Compared

CCTV inspection has been the standard for decades, and still matters for confirming what a low score is showing. But inspecting every foot of a large system with a camera truck on a regular cycle is expensive, slow, and requires certified operators with subjective opinions.

Factor	CCTV Inspection	Acoustic Assessment
Speed	Hundreds of feet per hour	18-20 thousand feet per day
Cost per foot	Higher, camera truck and crew time	A fraction of CCTV cost per foot
Crew Exposure	Contact with flow	Zero flow Contact
Output	Detailed visual record	Simple 0 to 10 pipe score
Best use	Confirming a specific defect	Screening an entire system quickly

Why the Combination Works Better Than Either Alone

The two methods are not competing. Acoustic Assessment shows where to look; CCTV shows what’s there. Pairing them sends the camera truck to a smaller, justified list of segments instead of running it blind.

Turning Acoustic Scores Into a Prioritized Cleaning and Repair Plan

A stack of scores alone does not fix anything. The value shows up once scores get mapped, ranked, and turned into a work order list.

From Raw Scores to a Ranked List

A well-run screening program sorts results by severity, so a small number of low scoring segments rise to the top while most of the system, usually in fine condition, gets left alone. That step makes the return on investment obvious, since crews stop cleaning pipe that isn’t dirty.

Inspecting Manholes

Acoustic Assessment requires opening every manhole, which provides an opportunity to inspect manholes and rank them as well. Manholes are inspected and each part of the manhole: collar, cover, barrel, invert, etc. receive a score of good, fair, or poor. Visible infiltration and linings are also flagged and photographs are taken.

Feeding the Data Into a GIS Dashboard

Scores mean more once they sit on a map next to other condition data. A ranked, tagged list is also easier to defend to a budget committee than a general claim that the system needs more funds.

Reducing Sanitary Sewer Overflows and Regulatory Risk

A blockage that goes unnoticed long enough can turn into a sanitary sewer overflow, bringing public health risk, environmental exposure, reporting obligations, and legal or regulatory actions most utilities would rather avoid. Regular acoustic screening catches a developing blockage while it is still a maintenance item, not an emergency.

Supporting Compliance Documentation

Many states require utilities to document maintenance frequency and justify it with actual condition, often under a Sanitary Sewer Management Plan. Acoustic screening produces that record: a dated, scored history, not a note that a crew walked by and it looked fine.

Real-World Results: What Utilities Report After Adopting SL-RAT

Independent research backs up what utilities say anecdotally. A U.S. EPA demonstration project found the technology showed real promise as a cost-effective way to handle pre-cleaning assessment and post-cleaning checks, freeing staff time for hands-on maintenance work. Separate industry analysis covering hundreds of millions of feet of screened sewer line found most segments tested come back in good condition, which is the whole case for screening first: calendar-based cleaning ends up servicing pipe that never needed it.

What Changes Operationally

Utilities that adopt this approach describe the same shift: fewer wasted truck rolls, a shorter cleaning list, lower water use, fewer carbon emissions, and fewer surprise overflows.

Integrating SL-RAT Into a Condition-Based Maintenance Program

Acoustic Assessment delivers the most value as a recurring input into a broader condition-based maintenance program, not a one time project. That means rescanning segments on a reasonable cycle and feeding results into the same system used to track manhole and pipe data.

Where It Fits Alongside Other Tools

Acoustic Assessment covers pipe segments. It does not replace interior manhole inspection or I&I detection, but it fills a gap those tools do not cover, telling a utility which pipes are flowing freely and which deserve a second look.

Smarter Screening, Stronger Systems: Why SL-RAT Belongs in Every Maintenance Plan

Sewer systems do not get younger, and budgets rarely grow to match aging pipe. SL-RAT sewer technology gives collection system managers a fast, low-cost way to know where their system stands today, not where an old schedule assumes it stands. That shift from calendar-based guessing to measured action separates a program that reacts to emergencies from one that prevents them.

RH Borden is a trusted wastewater technology provider based in Lehi, Utah, serving municipalities across the United States with advanced, data-driven sewer system maintenance solutions. We specialize in helping cities transition from traditional, labor-intensive maintenance to smarter, technology-enabled infrastructure management.

At RH Borden, we deliver innovative wastewater solutions including Acoustic Assessments using SL-RAT technology to quickly identify cleaning priorities, BASINiQ sensor networks for detecting inflow and infiltration (I&I) sources across sewer basins, and Manhole Virtual Models (MVM) that create digital twins of infrastructure assets to assess condition and guide rehabilitation decisions. Our solutions are designed to improve efficiency, reduce unnecessary maintenance costs, and extend the life of wastewater infrastructure through accurate, actionable data-driven insights.

Ready to see where your system’s biggest risks are actually hiding? Contact us today at 385-510-3223 or visit rhborden.com to learn more about our acoustic assessment and condition-based maintenance services.

Frequently Asked Questions

Is the SL-RAT a good fit for our system, or is it better suited to certain pipe conditions and utility sizes?

It designed for  gravity lines, 6 to 12 inches in diameter, and scales for both small and large systems. For larger systems with multple cleaning trucks and crews, Acoustic Assessment allows for optimized cleaning and manpower deployment. For smaller systems and those who contract out their maintenance, Acoustic Assessment may be the only way to proactively avoid sewer spills and.

How often should we rescan our system once we’ve done an initial acoustic assessment?

It depends on pipe age, material, and prior findings. Higher risk segments often get rescanned more frequently, while segments that consistently come back clear can wait longer. The magic of data is that it will tell you what is needed and provide a defensible plan for leadership and regulators.

What pipe sizes and materials can the SL-RAT actually assess?

It is designed for small to mid-diameter gravity lines and works across common materials like PVC, clay, and concrete. 

Does our own crew need training to run these assessments, or is this something we’d need to outsource?

Most systems are understaffed and choose to have Acoustic Assessment provided as a service. Where systems can run the tool themselves, training and equipment use is straightforward..

What kind of report or data do we actually receive after an assessment is complete?

Each Acoustic Assessment service includes pipe scores and manhole inspections delivered on an actionable GIS-based dashboard. Your team will receive a report of the findings and training on how to use the dashboard as well as recommendations going forward. Data gathered belongs to you and can be readily imported into your own systems.